This article seems to clarify a little bit about what actually happened on April 8th with the KLM flight's turnaround.

By the time the Boeing 747 had finished its three-hour crossing of the Atlantic, Homeland Security screeners were on high alert. The names of two Saudi passengers aboard the KLM flight had begun producing "hits" on the screening center's lists of 70,000 suspect foreigners.

The two Saudis, the database reported, were brothers and pilots who had attended the same Arizona flight school as 9/11 hijacker Hani Hanjour.

Interesting news story you add to it If the content is true. I have my doubts on it. In my opinion, the article makes too many asumptions to be credible.

When I read the Newsweek article I do not get really convinced of the safety meassures taken by the US. It states that the 2 Saudi's are "bad guys" and have Al Queda links. Why were they not arrested in the Netherlands? The US could simply have asked Dutch authorities to do so. The only thing they had to do is make clear to the Dutch justice that these 2 Saudi brothers are members of a terrorist organization and come up with proof of that. That would have allowed the Dutch to arrest them. In Holland it is not allowed to arrest people when you have no evidence against these persons. Dutch authorities did not have those and thus had to release the two persons. BTW the above is a hypothetical case and assuming it were "terrorists".

It still have doubts about how this incident has been handled. In the end the two persons have NOT been arrested and are free to go. This incident has been handled in a strange way. Maybe this incident is a good lesson for those parties involved that is not possible to win the war on terror by acting individually, but rather through cooperation and sharing information.

Perhaps there was a 'similar name' situation, that is, these people had the same names as or the bogus names of those on the watch list. That could explain why they were not arrested at AMS, as maybe they were able to confirm futher info that they were not the people whom were wanted on the list.
It is well established that many of those involved in 9/11 used alais names and got counterfit identity documents to get USA state driver licenses. Potential terrorists, criminals and despirate people have also used counterfit passports and stolen idenities to get false passports and visas to enter the country and later get drivers licenses. It is possible that the names on the list reflect alais names rather that the real names of wanted terror suspects. This has been and continues to be problem with such lists and not just to Islamic based terrorists, but European, ex-Soviet states/Russia and Asian non-Islamic terrorists.

What i'm curious about is what does the pilot tell the passengers as to why they are being denied entry into US airspace. I doubt they say "Well, because we have 2 potential terrorists onboard, we have to turn back." Does anyone have any info on that?